Ultrasonic Spectroscopy Study of Salad Dressings

Ultrasonic velocity and attenuation spectra (1 to 100 MHz) of salad dressings with different disperse phase volume fractions (φ= 0 to 0.394) and mean droplet radii (0.3 to 0.6 μm) were measured at 25 °C. There were significant differences between the experimental measurements and theoretical predictions due to droplet flocculation. The measured attenuation coefficient was lower than expected at low frequencies because of thermal overlap effects, but it was greater than expected at high frequencies because of scattering. These deviations could be accounted for using an effective medium theory. Results suggest that ultrasonic velocities at 14 MHz were independent of droplet size and could be used to measure droplet concentration of salad dressings.